1. Field of the Invention
The invention relates to binary recording and reproducing systems as well as to binary data transmission and receiving systems with particular reference to a system utilizing a non-consecutive zero code.
2. Description of the Prior Art
In prior art binary data recording and reproducing systems such as discs, drums and the like, binary input data is converted into a magnetic recording code which, in turn, is recorded on the magnetic medium. On readout the magnetic recording code is reconverted into the binary information for application to the utilization device. The reasons for the encoding and decoding as well as suitable magnetic recording codes are well known in the art. Conventionally, the magnetic recording code is written on the magnetic medium synchronously with regard to a clock pulse signal recorded on a clock track of the medium. For reasons well understood in the art, readout of the recorded code is synchronously effected usually with regard to a clock that is derived from the recorded code bits. The readout clock is conventionally derived from a phase locked oscillator loop that is continuously synchronized by the data. As is known, phase locked oscillators are complex, bulky, expensive and critical circuits having significant power requirements and not particularly well suited to environments where space, weight and cost are primary factors. Such an environment may, for example, be in airborne equipment such as that described in applicants' assignee's U.S. Pat. No. 3,864,784 entitled "Magnetic Disc Memory" and in copending patent applications Ser. No. 577,970, filed May 15, 1975 in the names of D. H. Duncan, C. T. Herdman and T. V. Littlejohn entitled "Magnetic Disk Memory"; Ser. No. 581,987, filed May 29, 1975 in the names of W. C. Post and E. E. Olive entitled "Steered Lateral Course Transition Control For Aircraft Area Navigation Systems"; Ser. No. 581,988, filed May 29, 1975 in the names of D. H. Baker, L. J. Bowe and W. C. Post entitled "Helical Vertical Path Control For Aircraft Area Navigation System"; and Ser. No. 598,904, filed July 24, 1975, in the names of D. H. Baker, L. J. Bowe, K. P. Manning and W. C. Post entitled "Vertical Path Control For Aircraft Area Navigation System."
Not only do phase locked oscillator loops suffer from the disadvantages discussed above but such devices are also subject to frequency drift and hence desynchronization when the spacings between the synchronizing bit transitions of the recording code are excessive.
An additional problem in the prior art is that known codes suitable for adequate clock generation utilizing phase locked oscillator loops are generally not adequately efficient, i.e., a maximum number of information bits mapped into a minimum number of recording code bits for the properties desired.